The invention relates to an expansion catheter for bypass surgery and serves for insulating the anastomosis region in which a bypass is sewed to a defective blood vessel.
During bypass operations a bypass is connected to a blood vessel displaying a stenosis, the bypass bridging the stenosed section of said blood vessel. Normally the heart is put out of action and the pumping function of the heart is assumed by a heart-lung machine during such an operation so that the surgeon can unimpededly operate the blood vessel. However, operations carried out with the heart put out of action are risky and impose a strain on the patient""s body.
In the case of the minimal-invasive bypass surgery the bypass operation is carried out with the heart beating. The connecting point for the bypass is opened by an incision and the bypass is connected there. However, this involves the risk of heavy bleeding; further, the conditions for operations carried out with the heart beating are much harder than those for operations carried out with the heart put out of action.
It is also common practice to dilate blood vessels by a balloon catheter to expand straits. For this purpose perfusion catheters may be used which allow a continuous blood flow through the balloon area to be maintained during dilatation. In this way blocking of the blood vessel concerned during the dilatation is prevented.
In DE 32 35 974 A1 a balloon catheter having two balloons arranged at an axial distance is described. The balloon cathether is adapted to be inserted into a blood vessel. By expanding the balloons the vessel region between the balloons is insulated. To allow the blood to flow the balloon catheter is provided with a perfusion duct bridging the balloon area. Substances are injected into the insulating area which dissolve or pulverize deposits in the vessels.
From DE 195 09 464 C1 a vessel implant is known which comprises an anchoring part and a functional part forming a continuous tubular stent of wire fabric or wire mesh. Between anchoring part and functional part there is a constriction whose walls form a thrombosis filter. The vessel implant is elongated under elastic deformation such that it contracts in radial direction. In this condition it is mounted on a catheter and fixed by means of a supporting tube resting against it from outside. In the blood vessel the implant is released by withdrawing the supporting tube such that the anchoring part can expand and fit from inside to the vessel wall at an elastic bias. Contraction of the vessel implant is not envisaged.
Further, vessel supports are known which are referred to as stents. Such vessel supports are made of wire material. They are inserted by a catheter into the blood vessel and then plastically expanded such that, in the expanded condition, they keep the blood vessel open. Such stents also include reversibly expandable stents. The latter are extended from a catheter tube and then automatically expand due to their elasticity. If the catheter is subsequently mounted on the stent, the stent contracts and is retracted into the catheter tube. Such stents normally serve for expanding a stenosis.
It is the object of the invention to provide an expansion catheter which can be used to insulate a wall section of a blood vessel without blocking passage of the blood through the blood vessel.
The expansion catheter according to the invention comprises a reversibly expandable stent which, in the expanded condition, has at least two expansion zones space apart from each other and an intermediate constriction. In the expanded condition the expansion zones of the stent are pressed against the vessel wall. Between the two expansion zones the vessel wall is relieved, i. e. it is not subjected to internal pressure. The stent ensures that temporarily no blood pressure acts upon the vessel wall to allow an anastomosis (seam) to be produced on the vessel wall or similar surgical interventions to be performed. The stent is not used as a vessel support but for temporary blocking of the blood flow.
The stent is a latticed metal structure adapted to expand and contract in radial direction. In the expanded condition said metal structure is permeable to blood and thus not suited for complete sealing.
According to a preferred embodiment of the invention the stent is provided with an envelope over at least a portion of its length. Said envelope renders the wall of the stent impermeable to liquids and thus effects a considerable draining of the vessel wall in the constriction area of the stent.
It is of advantage if the stent ends at its distal end in an open expansion zone. This reduces the risk of thrombosis which occurs in the case of formation of heavy eddies caused by the constrictions. Although the blood flow is accelerated when it passes the constriction, it decelerates again inside the distal expansion zone.
After the surgical intervention on the vessel wall the stent contracts again and is retracted into the catheter tube. Thus the stent does not stay in the blood vessel but is removed together with the catheter tube from the patient""s body.
The stent may be configured such that it has a shape memory which sets it into the expanded condition unless a restraint is applied from outside. Alternatively, the stent may be configured such that it is set into the expanded condition by application of an external restraint, e. g. by upsetting in axial direction. In any case, the stent comprises at least two expansions zones in the expanded condition.
Hereunder a preferred embodiment of the invention is explained in detail with reference to the drawings in which: